Safety valve

ABSTRACT

A safety valve of the type that includes a sleeve (1) with a high pressure port (11) and a low pressure port (12); a valve seat (2) and a poppet (3), both slidably inserted in the sleeve and adapted to be brought together to provide a valve interface that is capable of establishing and blocking a fluid communication between the high pressure port and the low pressure port; and a spring (7) adapted to force the poppet against the valve seat, wherein a difference in force between a fluid pressurized in the high pressure port acting on a pressure receiving surface of the poppet and the spring acting against said pressurized fluid urges the poppet to open the valve interface, thereby relieving the high pressure port by a portion of the pressurized fluid admitted out thereof into the low pressure port. The safety valve comprises a damper chamber (A) formed between the sleeve and the valve seat mentioned above, whose volume is reduced by a sliding movement of the valve seat against the action of the above mentioned spring; and a constriction adapted to bring the damper chamber into fluid communication with a low pressure side, the constriction (35) having an area of the fluid communication that is variable in such a way that it may be reduced by a sliding movement of the valve seat against the action of the spring and that it may be increased by a sliding movement in an opposite direction of the valve seat under the action of the spring.

TECHNICAL FIELD

The present invention relates to a safety valve that is adapted for usein a hydraulic circuit such as those for supplying a discharge pressurefluid from a hydraulic pump into a hydraulic motor.

BACKGROUND ART

There has been known in the art a hydraulic circuit for supplying adischarge pressure fluid of a hydraulic pump into a hydraulic motor, inwhich the discharge pressure fluid of the hydraulic pump is supplied viaan operating valve into one of a pair of principal circuits, of which afirst is connected to a first port of the hydraulic motor and a secondis connected to a second port of the hydraulic motor.

In a hydraulic circuit of this type, it is customary to use a safetyvalve of modulation type that is designed to make a relief of a portionof fluid of pressure elevated in the first and second principal circuitsto ensure that the elevated pressure may not exceed a pre-establishedpressure, so that when the hydraulic motor is either to start or to stopdriving, fluid pressure in the first or second principal circuit whichis active may slowly be elevated in order to diminish a shock that canthen be disadvantageously brought about therein. Such a safety valve asknown in the art, that is capable of performing a modulation operationin which fluid pressure may rapidly be elevated up to a modulation startpressure and after then slowly be elevated up to a preset pressure, isshown in FIG. 1 of the drawings attached hereto.

More specifically, the safety valve has a valve seat 2 slidably insertedin a sleeve 1 in which a poppet 3 is also slidably inserted so that aconcave conical surface 5 of the poppet 3 may be thrusted by a spring 4against a convex conical surface 6 of the valve seat 2 to provide avalve interface. A piston 7 is slidably inserted in the poppet 3 to forma chamber 8 which is in fluid communication via a small opening 9 andvia an inner bore 10 of the valve seat 2 with a high pressure port 11whereas a low pressure port 12 is formed in the sleeve 1.

And, the sleeve 1 is formed at an end thereof with a large diametersection 20 whose open end has a plug 21 securely fitted therewith. Thevalve seat 2 is shaped to provide a stepped peripheral configurationhaving a small diameter one end portion 22, a large diameter mid portion23 and an intermediate diameter opposite end portion 24. The smalldiameter one end portion 22 is inserted in the plug 21 to fit with aninner surface 21a thereof and is then sealed with a sealing material 25,whereas the large diameter mid portion 23 is inserted in the sleeve 1 tofit with the large diameter section 20 thereof and is then sealed with asealing material 26. And, the intermediate diameter opposite end portion24 is inserted in the sleeve 1 to fit with its inner surface 1a. Thus,the valve seat 2 is allowed to axially be slid and be displaceable by adistance L. Besides, the large diameter mid portion 23 and the sleeve 1are shaped to provide an annular space 27 between the large diameter midportion 23 and a step portion 1b of the sleeve 1. The annular space 27is opening to the low pressure port 12 via an interstice 28 between thesleeve inner surface 1a and the intermediate opposite end portion 24,which is here designed to form a damper chamber A.

Let it be assumed that the section in which the valve surface 5 and theseating surface 6 are to be in contact with each other has a diameterd1, the piston 7 has a diameter d2, and the small diameter one endportion 22 of the valve seat 2 has a diameter d3.

An explanation is now given below of an operation of the conventionalsafety valve whose construction has been described above.

Assuming that the high pressure port 11 has a pressure that rangesbetween P1 and 0, the spring 4 forces the poppet 3 which in turn pushesthe valve seat 2 to cause it to move by the distance L1 leftwards in theFigure to contact with the plug 21. Here, it should be noted that thespring load F1 of the spring 4 is set at a value that is lower than aconventional value by L1×K where K is a spring constant.

Under the state described, if the pressure P1 in the high pressure port11 is suddenly elevated, the poppet 3 starts sliding rightwards when athrust force due to the pressure P1 acting on the pressure receivingsurface of the poppet 3 with an area A1=π/4·(d₁ ² -d₂ ²) is balancedwith the spring load F0 and then causes a section between the valvesurface 5 and the seating surface 6, that is, the valve interface toopen, thereby permitting a fluid of the elevated pressure to commencebeing admitted into the low pressure port 12, thus relieving the highpressure port 11. The pressure at this instant is a modulation startpressure.

Then, with the elevated fluid pressure P1 acting on the end surface 2aof an area A2=π/4·(d₃ ² -d₁ ²) of the valve seat 2, the valve seat 2 isplaced under a thrust force=A2×P1 to tend to move rightwards. However,also under the action of the damper chamber A, that is, the action inwhich pressure fluid in the annular space 27 is restricted in its flowby the interstice 28, flowing out of it and gradually into the lowpressure port 12, the valve seat 2 must be more slow to move rightwardsthan the poppet 3. As a consequence, the pressure rises with a reducedslope towards arriving at a preset pressure when the seating surface 6is urged to contact the valve surface 5.

The pressure of fluid in the high pressure port 11 under such a reliefaction will thus be to assume a waveform as represented by the solidcurve shown in FIG. 2, rising in two stages with a long time elapseduntil the preset pressure is reached.

With such a safety valve, it is therefore seen that a drop of pressurein the high pressure port 11 while it is under a relief action causesthe poppet 3 and the valve seat 2 to move leftwards with the spring 4,returning to their initial positions. As the valve seat 2 is movedleftwards, fluid in the low pressure port 12 is forced to flow via theinterstice 28, sucked into the damper chamber A.

However, since the interstice 28 that must be small and minimum in orderto retard the rightward movement of the valve seat 2 impedes the fluidflowing that is sucking into the damper chamber A, the fluid fails to besucked into the damper chamber A to an extent that is proportionate tothe rate at which the valve seat 2 is moving leftwards via the poppet 3with the spring 4. A negative pressure then is caused in the damperchamber A and gives rise to the formation of air bubbles therein.

The rightward movement of the valve seat 2 produced by rising ofpressure again in the high pressure port 11 while air bubbles are formedin the damper chamber A causes the air bubbles to tend to be broken inthe damper chamber A, allowing the valve seat 2 to be displacedrightwards quicker than at a rate that is solely governed by the flowrestrictive action of the interstice 28. It follows then that a desiredlength of the time of modulation (i. e., the time elapsed from theinstant at which the pressure is at a modulation start pressure until aninstant at which the pressure reaches a preset pressure) cannot beachieved.

It can also be seen that since the damper chamber A is in fluidcommunication with the low pressure port 12 via the interstice 28between the inner surface 1a of the sleeve 1 and the intermediatediameter opposite end portion 24 of the valve seat 2, a change in thediameter of either of the sleeve 1 and the valve seat 2 as caused by achange in temperature alters the size of the interstice 28. The size ofthe interstice 28 also fluctuates when the sleeve 1 or the valve seat 2is eccentric. Such a change or fluctuation in the size of the interstice28 bars a stabilized time span of modulation from being obtained.

As observed in the foregoing description, it has hitherto beenrecognized in the art to be difficult to adjust the time of modulationto be sufficiently long while the interstice 28 is kept minimum, whichin turn makes it difficult to significantly diminish a shock that isentailed in a hydraulic motor when it is to start or end driving.

It is accordingly an object of the present invention to provide a safetyvalve which can overcome the problems mentioned above.

SUMMARY OF THE INVENTION

In order to achieve the above mentioned object, there is provided inaccordance with the present invention in a certain aspect thereof asafety valve that includes:

a sleeve having a high pressure port and a low pressure port;

a valve seat and a poppet, both slidably inserted in the sleeve andadapted to be brought together to provide a valve interface that iscapable of establishing and blocking a fluid communication between thehigh pressure port and the low pressure port; and

a spring adapted to force the poppet against the valve seat,

wherein a difference in force between a fluid pressurized in the highpressure port acting on a pressure receiving surface of the poppet andthe spring acting against the pressurized fluid urges the poppet to openthe valve interface, thereby relieving the high pressure port by aportion of the pressurized fluid admitted out thereof into the lowpressure port,

and is characterized in that

the safety valve comprises:

a damper chamber formed between the said sleeve and the said valve seatand having a volume thereof, wherein a sliding movement of the saidvalve seat against the action of the said spring reduces the volume ofthe said damper chamber; and

a constriction adapted to bring the said damper chamber into fluidcommunication with a reduced pressure side, the said constriction havingan area of the fluid communication that is variable in such a way thatit may be reduced by a sliding movement of the said valve seat againstthe action of the said spring and that it may be increased by a slidingmovement in an opposite direction of the said valve seat under theaction of the said spring.

According to the construction mentioned above, it can be noted andshould be understood that the constriction which permits fluid in thedamper chamber to flow out of it and to a reduced pressure side and ofwhich the area of fluid communication is reduced when the valve seat isslid under a pressure elevated in the high pressure port against thespring action is allowed to slide so slowly, thus causing it to takelonger time for the pressure to rise from a relief start pressure up toa preset pressure, hence a prolonged time of the modulation that ensues.

Also, it can be seen and should be appreciated that the constrictionthrough which fluid in the reduced pressure side is sucked into thedamper chamber and whose area of communication is increased when thevalve seat is slid under the spring force with the pressure reduced inthe high pressure port allows the fluid in the reduced pressure side toflow into the damper chamber smoothly, thereby preventing the damperchamber from becoming negative in pressure inside and from producing airbubbles therein.

This provides a pre-established time of modulation that results if thesafety valve is brought iteratively into a relief action. Consequently,this safety valve, used in a hydraulic circuit for supplying apressurized fluid into a hydraulic motor, significantly diminishes ashock which occurs when the motor starts and stops driving.

It is yet possible to further prolong, without any inconveniencesuffered, the time of modulation in which the valve seat is even moreslowed in its sliding movement with the constriction having the area offluid communication further reduced when the valve seat is slid againstthe spring action. But, even so the constriction can have its area offluid communication enlarged when the valve seat is to be slid under thespring force, without regard to how far the area of fluid communicationwas then reduced.

By virtue of the fact that a further longer time of modulation does notallow air bubbles to be generated in the damper chamber, this safetyvalve if operated with a repeated relief action does not fail toeffectively operate in any prolonged time of modulation that isnecessary and sufficient. Therefore, the safety valve according to thepresent invention is adapted for use in a hydraulic circuit forsupplying a pressure fluid into a hydraulic motor while attainingsignificant reduction of a shock occurring when the hydraulic motor isstarting or stopping a drive.

In the construction described above, it is desirable that the saidconstriction comprise:

a stepped bore having a small diameter section and a large diametersection;

a ball adapted to be fitted in the said stepped bore; and

a spring, which is separate from the first mentioned spring, forthrusting the said ball against the said small diameter section,

wherein the said small diameter section is in fluid communication withthe said reduced pressure side and the said large diameter section is influid communication with the said damper chamber.

According to the construction mentioned above, it can be noted andshould be understood that an area of fluid communication as referred tois established by the diameter of the stepped bore and the diameter ofthe ball. Thus, a constriction with such an area of fluid communicationas so established becomes analogous to a sharp edge orifice, presentingno change in constriction property (i. e. area of fluid communication)against a change in temperature. Hence, a stabilized time span ofmodulation is provided.

In addition to the constructive elements mentioned above, the safetyvalve according to the present invention may include a piston that isinserted in the said poppet to provide a chamber, a narrow opening thatis formed in the said poppet and is in fluid communication with the saidhigh pressure port, and a throughgoing bore that is formed in the saidvalve seat.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will better be understood from the followingdetailed description and the drawings attached hereto showing certainillustrative embodiments of the present invention. In this connection,it should be noted that such embodiments as illustrated in theaccompanying drawings are intended in no way to limit the presentinvention but to facilitate an explanation and understanding thereof.

In the accompanying drawings

FIG. 1 is a cross sectional view that shows a safety valve in the priorart;

FIG. 2 is a graph that shows relief characteristics of safety valves ofmodulation type;

FIG. 3 is a cross sectional view that shows an embodiment of the safetyvalve according to the present invention;

FIG. 4 is an enlarged cross sectional view that shows a constriction inthe embodiment shown in FIG. 3; and

FIG. 5 is a cross sectional view taken along the line V--V in FIG. 4.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, suitable embodiments of the present invention with respectto a safety valve are set forth with reference to the accompanyingdrawings hereof.

An explanation is given of an embodiment of the present invention basedon FIG. 3. It should be noted that the same components as those in theprior art are designated by the same reference characters and a furtherexplanation of details thereof are here omitted.

A plug 21 is interiorly formed with a bore having a small diametersection 30 and a large diameter section 31. The plug 21 is fitted withan end of the sleeve 1 to fit over an outer peripheral surface 1cthereof in the large diameter bore section 31. The small diameter oneend portion 22 of the valve seat 2 formed at one end thereof asmentioned previously is fitted with the small diameter section 30 of theplug 21 interiorly thereof and is sealed thereto with a sealing material32. The large diameter mid portion 23 of the valve seat 2 is fitted withthe large diameter section 31 of the plug 21 interiorly thereof and issealed thereto with a sealing material 33. The intermediate diameteropposite end portion 24 formed at the other end thereof is fitted withthe inner peripheral surface 1a of the sleeve 1 and is sealed theretowith a sealing material 34.

A damper chamber A which is constituted by an annular space 27 is hereformed by the large diameter section 31 of the plug 21, an end surface1d of the sleeve 1 and the intermediate diameter opposite end portion 24of the valve seat 2 together so as to be in fluid communication via aconstriction 35 with an auxiliary low pressure port 36 that is formed inthe small diameter bore section 30 of the plug 21.

Referring to FIG. 4, an explanation is given of a detailed structure ofthe constriction 35.

The large diameter mid portion 23 of the valve seat 2 is formed with anannular groove 40, and also includes a round portion 41 lying closer tothe damper chamber A than the annular groove 40, which is smaller indiameter than the large diameter section 31 of the plug 21. An annularslit 42 is formed between the round portion 41 of the valve seat 2 andthe large diameter section 31 of the plug 2 to provide a fluidcommunication between the damper chamber and the annular groove 40. Theannular slit 42 is so much of size that it may not affect the time ofmodulation.

The annular groove 40 is formed with a stepped bore 45 having a smalldiameter section 43 and a large diameter section 44 and has a ball 46fitted therein. In the stepped bore 45, the small diameter section 43has a diameter D1, the large diameter section 44 has a diameter D2, andthe ball 46 has a diameter D3 which is a bit smaller than the diameterD1 of the small diameter section 43. Further, the small diameter section43 has a depth L2 which is a bit greater than one half (1/2) of thediameter D3 of the ball 46.

A spring 47 is also provided that is ring shaped and wound fittedly inthe annular groove 40 to force the ball 46 against the bottom wall ofthe stepped bore 45. A fluid bore 48 is further formed which provides afluid communication of the small diameter section 43 in the stepped bore45 with the auxiliary low pressure port 36 via a space 49. The space 49lies between one end surface of the large diameter mid portion 23 of thevalve seat 2 and the large diameter bore section 31 of the plug 21 andalways communicates with the auxiliary low pressure port 36 via aninclined surface 23a of the large diameter mid portion 23.

An explanation is next given of the operation of the embodimentdescribed.

When the pressure in the high pressure port 11 rises to a modulationcommencing pressure, in the same manner as with the conventional safetyvalve previously described, the poppet 3 is displaced rightwards againstthe spring action of the spring 4 to commence relieving the highpressure port 11 by pressure fluid admitted out thereof into the lowpressure port 12. Thereafter, the valve seat 2 is displaced rightwardsunder the pressure in the high pressure port 11 to allow fluid in thedamper chamber A to flow through the annular slit 42, the annular groove40, an interstice between the large diameter section 44 and the ball 46and an interstice between the small diameter section 43 and the ball 46into the fluid bore 48 and then through the latter and the space 49 intothe auxiliary low pressure port 36.

The pressure fluid that flows out of the damper chamber A towards theauxiliary low pressure port 36, in the course of passing through a smallinterstice provided by the small diameter section 43 and the ball 46that serves as a restrictor or constrictor, is restricted or constrictedin flow with less fluid flow admitted therethrough and out thereof. Inother words, a small difference in diameter between the small diametersection 43 and the ball 46 provides a reduced area of fluidcommunication between the damper chamber A and the auxiliary lowpressure port 36, hence a reduced flow of fluid that is admitted intothe auxiliary low pressure port 36 from the damper chamber A. Thiscauses the valve seat 2 to be displaced rightwards at a reduced speed,which in turn causes the pressure to rise at a reduced rate up to apreset pressure. Hence, a prolonged time of modulation ensues.

Specifically, a flow constriction as described above is provided by aninterstice formed between a circular rim defined by the ball 46 cut by ahorizontal plane at a height of its radius as shown and the wall of thesmall diameter orifice 43. Thus, such a constriction is considered to beessentially equivalent to one in a sharp edge orifice in general, therebeing no significant change in constrictive characteristics with respectto a change in temperature. It should also be noted that the pressurizedfluid passing over the ball 46 to allow it to be rotated serveseffectively to expel a foreign matter that may possibly have beenentrapped in the interstice.

It can also be seen that if the pressure in the high pressure port 11 isreduced, the valve seat 2 is displaced leftwards under the action of thespring 4. Fluid is then caused to flow through the low pressure port 36,the space 49 and the fluid bore 48 into the small diameter section 43and then, pushing up the ball 46, to pass through a large intersticecreated between the large diameter section 44 and the ball 46, flowinginto the annular groove 40 and through the latter and the annular slit42 into the damper chamber A.

The enlarged interstice in this case in which fluid flows in theopposite direction provides a larger area of fluid communication betweenthe low pressure port 36 and the damper chamber A and allows the fluidmuch more to flow into the damper chamber A without restriction,permitting the seat valve 2 to quickly return to its initial state.Thus, the inside of the damper chamber A is effectively prevented frombecoming negative in pressure and hence is freed from a formation ofbubbles therein.

There is thus provided a safety valve which may be used in a hydrauliccircuit for supplying a hydraulic motor with a pressure fluid whereby ashock occurring when the motor is to start or stop driving is markedlydiminished.

While the present invention has hereinbefore been set forth with respectto certain illustrative embodiments thereof, it will readily beappreciated by a person skilled in the art to be obvious that manyalterations thereof, omissions therefrom and additions thereto can bemade without departing from the essence and the scope of the presentinvention. Accordingly, it should be understood that the presentinvention is not intended to be limited to the specific embodimentsthereof set out above, but to include all possible embodiments thereofthat can be made within the scope with respect to the featuresspecifically set forth in the appended claims and encompasses all theequivalents thereof.

What is claimed is:
 1. A safety valve including:a sleeve having a highpressure port and a low pressure port; a valve seat and a poppet, bothslidably inserted in the sleeve and adapted to be brought together toprovide a valve interface that is capable of establishing and blocking afluid communication between the high pressure port and the low pressureport; and a spring adapted to force the poppet against the valve seat,wherein a difference in force between a fluid pressurized in the highpressure port acting on a pressure receiving surface of the poppet andthe spring acting against the pressurized fluid urges the poppet to openthe valve interface, thereby relieving the high pressure port by aportion of the pressurized fluid admitted out thereof into the lowpressure port, wherein the safety valve comprises:a damper chamberformed between said sleeve and said valve seat and having a volumethereof, wherein a sliding movement of said valve seat against theaction of said spring reduces the volume of said damper chamber; and aconstriction adapted to bring said damper chamber into fluidcommunication with a reduced pressure side, said constriction having anarea of the fluid communication that is variable in such a way that itmay be reduced by a sliding movement of said valve seat against theaction of said spring and that it may be increased by a sliding movementin an opposite direction of said valve seat under the action of saidspring.
 2. A safety valve as set forth in claim 1, characterized in thatsaid constriction comprises:a stepped bore having a small diametersection and a large diameter section; a ball adapted to be fitted insaid stepped bore; and a spring, which is separate from the firstmentioned spring, for thrusting said ball against said small diametersection, wherein said small diameter section is in fluid communicationwith said reduced pressure side and said large diameter section is influid communication with said damper chamber.
 3. A safety valve as setforth in claim 1, further comprising a piston adapted to be insertedinto said poppet to provide a chamber; a narrow opening that is formedin said poppet and is in fluid communication with said high pressureport, and a throughgoing bore that is formed in said valve seat.
 4. Asafety valve as set forth in claim 2, further comprising a pistonadapted to be inserted into said poppet to provide a chamber; a narrowopening that is formed in said poppet and is in fluid communication withsaid high pressure port, and a throughgoing bore that is formed in saidvalve seat.